Surface migration of branched molecules: Analysis of energeticand entropic factors

• Published in: The Journal of chemical physics 2005-10, Vol.123 (14), p.144902-144902-9
• Main Authors: Minnikanti, Venkatachala S., Archer, Lynden A.
• Format: Article
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.2052627

We have introduced energetic factors into the response theory developed by Wu and Fredrickson [ Macromolecules 29 , 7919 ( 1996 ) ] to predict the enrichment of branched molecules due to architectural effects at surfaces. This development simultaneously increases the utility of the theory for guiding experimental investigations, and makes possible a rigorous assessment of theoretical predictions in careful studies of isotopically labeled linear/branched species binary blends at surfaces. For example, the introduction of energetic factors allows us to predict the existence of a crossover molecular weight, below which an energetically unfavorable species at a surface can be enriched entirely due to architecture. For binary blends of linear chains, the degree of polymerization (Kuhn) of the energetically unfavorable species at the crossover point is r c ≅ 2 U e ∕ Δ U s . Here, U e is the attraction of chain ends towards the surface and Δ U s is the difference in the interaction potential of main chain segments to the surface due to chemical differences and/or isotopic labeling. We also show that surface segregation of an additive in a host polymer due to architectural effects alone is significantly enhanced as the spinodal temperature of a branched/linear blend is approached. Detailed comparisons of the modified response theory with lattice simulations are used to evaluate the theory and to determine the limits of its applicability.